1. Field of the Invention
The present invention relates to a microfilm scanner which searches or retrieves a target frame from a strip-shaped microfilm, reads an image in the target frame using a line sensor, and outputs data representing the read image to a CRT or a printer. The present invention also relates a control method for this microfilm scanner.
2. Description of the Prior Art
There is a known microfilm scanner, which searches or retrieves a target frame from a strip of microfilm such as a roll film and reads an image projected from the target frame using a line sensor. There is also proposed a microfilm reader which uses the above microfilm scanner in combination with an output device such as a CRT display or a printer.
The use of the line sensor to read an image makes it easier to process the image as digital image signals, to display it onto a CRT or a liquid crystal display panel, or to output it to a printer. This also makes it easier to store data representing the read image into a memory such as a magneto-optical disk or to transfer the image data to other image processor. Therefore, the read image can be widely used.
In a microfilm formed in a band, tape, ribbon or long strip shape, such as a roll film, search or retrieval marks such as blips are generally provided or recorded within a given range of an edge side. Therefore, the given range from each edge of the film is defined as a region for search marks and an image is photographed on the remaining range between both edge-side regions. Thus photographed image constitutes a frame containing an original or document image.
When reading an image in a target frame using such a microfilm scanner, it may be appreciated that the entire area except the search-mark regions scanned with high density, that is, it will be desirable to be able to read only image signals in the image photographed region with high density for use as image data to be output. It is therefore necessary to correctly discriminate a range occupied by photographed image frames from a range occupied by search marks. In the conventional microfilm scanner, however, the operation procedure such as for discriminating therebetween is made complicated.
For example, when the image photographed on the microfilm is a negative image, the background portion in each original image is blackened and white frame region surrounds each original image. When a negative image is reversed to make it a positive image, the above mentioned white frame region turns to the blackened frame region. In this specification, such portions other than the original image region in the frame are called a black frame. On the other hand, search marks or blips are typically black spots or markers on the edge of the negative-positive reversed film, one spot or marker for each frame. Therefore, the black frames and the search marks are often confused with each other. As a result, the detection accuracy of the microfilm scanner is lowered and thereby a range including the target frame may not be detected.